Project Summary/Abstract Animal-Assisted Interventions (AAI) can increase social behavior in children with autism spectrum disorder (ASD), although the mechanism by which this occurs remains elusive. The central goal of this project is to identify the mechanisms involved in the social-enhancing effect of dogs on children with ASD. We will incorporate therapy dogs into an established evidence-based, group social skills instruction program for children with ASD, using a controlled experimental design with between- and within- subject comparisons and physiological and behavioral outcome measures. We predict therapy dogs to have a specific and measurable effect on children's social behavior and that this effect is gained through identifiable mechanisms. Specifically, we hypothesize that (1) an integration of therapy dogs into group social skills instruction will result in reduced stress and improved social behavior compare to traditional group instruction; (2) repeated exposure to the therapy dog across sessions will increase a child's preference for spending time with the dog and will increase the social-enhancing effects of the dog; and (3) that the therapists will experience less stress, engage in more social and affiliative behavior towards the children, and deliver higher quality instruction during sessions that include dogs. We will enroll 72 children with ASD into group social skills instruction classes taught by 6 therapists. Each child will experience a 10-week, 8-student class in which either (a) the first 5 weeks will involve a therapy dog, (b) the last 5 weeks will involve the therapy dog, or (c) the class will not involve a therapy dog. The therapists will teach the courses repeatedly across the three cycles of the program with different children, rotating through each condition. Social behavior, stress behavior, heart rate, electrodermal activity, and salivary cortisol concentrations of children and therapists will be assessed and compared across conditions. The direction of the children's social behavior towards the dog and peers and the changes in quality of instruction of therapists during dog sessions compared to no-dog sessions will also be assessed. The outcomes of this research will lead to significant enhancements in current interventions for individuals with ASD.